The invention relates to a process for pelletizing or granulating ammonium sulfate.
Synthetic fertilizers are usually sold in grain sizes of pellets which are as uniform as possible. It is, however, desirable for modern fertilizers to intermix different fertilizer components in order that the fertilizer mixture can thus be applied to the land. This type of mixed fertilizer is being supplied in most cases directly from the manufacturer. This notwithstanding, it is desirable during the manufacturing process to make the individual components of such fertilizer mixture separately in order to permit later to mix them in any desired ratio.
During shipment, however, there arise problems with this kind of mixture since the different components of the mixed fertilizer have a tendency, due to their physical properties, to separate out during shipping when they are exposed to shaking or vibration.
The main reason for these separations is the grain size. However, the grain shape is also important. It can therefore happen that a load of mixed fertilizers arrives at the final user, largely in separate components. A uniform distribution of the fertilizer is then no longer possible.
These problems appear particularly if not only the grain size, but also the grain shape varies. Ammonium sulfate normally is supplied in crystallized condition. These crystals, in addition, are in most cases considerably smaller than the normal commercial grain sizes of pelletized fertilizers.
The mixture of ammonium sulfate with other fertilizer components presents, therefore, a difficult problem.
It is on the other hand also known that ammonium sulfate does crystallize only with certain difficulties and the manufacture of large crystals which would be desirable according to the above discussion is therefore rather costly. Besides, if it were possible even to make large ammonium sulfate crystals they still would have a considerably different shape when compared with pelletized fertilizers. Therefore, the danger of separation still exists.
Experiments to convert crystallized ammonium sulfate into pellets have heretofore not had any commerically useful result.
In a prior art fuel-gas desulfurization process (West German published application No. 25 18 386) a spray dried ammonium sulfate is obtained during the process in the form of a fine powder which separates out in an electrofilter and is obtained therefrom. This product was, however, not suited for use in fertilizers in the dust form in which it was obtained since then similar problems occurred as above described.
It is, therefore, an object of the present invention to convert this type of dust-like product into a fertilizer or fertilizer component which can be obtained with normal chemical appliances and procedures.